Interferons (IFNs) and retinoids are powerful biological response modifiers. Although they are effective growth inhibitors of certain transformed cells, both these agents have limited efficacy as single agents against many tumors. However, they strongly inhibit the growth of several tumor cells when used in combination. We have shown that the IFN-beta+retinoic acid (IFN/RA) combination synergistically inhibits the growth of a variety of breast and other tumors both in vitro and in vivo. More importantly, IFN/RA is cytotoxic to several breast tumor cell lines. Clinical studies also demonstrated potent tumor inhibitory effects of IFN/RA. In the light of this data, it becomes important to understand the changes in gene expression that lead to tumor growth suppression. Previous studies did not suggest a role for known growth inhibitory gene products in IFN/RA induced cell death. Therefore, we hypothesize that IFN/RA combination employs either novel or hitherto unimplicated gene products for inducing cell death. During the last funding period the principal investigator's laboratory identified several candidate genes, Genes associated with Retinoid-IFN induced Mortality (GRIM) that participate in cell death, using a Suppression of Mortality by Antisense Rescue Technique (SMART). SMART permits the isolation of cell death associated genes on the basis of their function within tumor cells. In this proposal we will characterize the mechanism of GRIM action and their relationship to terminal tumor cell death regulators. The proposal will also examine the relevance of GRIMs for cancer therapy in an animal model. These studies are important because GRIMs may: i) represent novel tumor suppressors, ii) serve as markers for disease status and therapeutic response, iii) play a role in death of other cancer types, and iv) be useful in gene therapy. Our understanding of cancer cell death and growth pathways is far from complete. Although discovered by virtue of their role in IFN/RA induced tumor cell death, GRIMs may participate in other physiologic or therapeutic-induced death pathways. Characterization of GRIMs may permit a rational drug design for cancer therapy. Identifying the mechanisms of GRIM inactivation may help understand the therapeutic resistance. Thus, the proposed studies will contribute novel information to the understanding of cancer cell biology and therapy. This proposal is a translational study that provides a basis and the necessary reagents for future phase II trials with IFN/RA or other drug combinations for cancer therapy.